Rotor guard for centrifugal compressor

ABSTRACT

A safety device to protect a rotor impeller in a centrifugal compressor from damage that might otherwise occur when the impeller, because of some fault, engages an opposed wall of its chamber. The device includes a hollow tubular body supported in the walls of the compressor. It has one end connected with a pressure switch arranged in a power control electrical circuit, and has an opposite abradable thin end projecting into the impeller chamber. The device is pressurized with fluid and, when its thin end is caused to be abraded away by the impeller, the pressure fluid will be dumped, causing actuation of the switch and consequent discontinuance of power to the compressor. The pressure fluid for the device may be supplied from the compressor system or from an external source. In condenser steam turbines, the tubular body of the device may be connected with a vacuum element and arranged so that when the thin end is abraded away the tubular body will become pressurized by the process fluid to cause actuation of the pressure switch.

United States Patent [72] Inventors Ernest W.Blattner Franklin, Pm;

Arnold M. Heitmann, Swampscott, Mass. [21] Appl. No. 830.291 [22] FiledJune 4, 1969 [45] Patented July 6, 1971 [73] Assignee Chicago PneumaticTool Company New York, N.Y.

[54] ROTOR GUARD FOR CENTRIFUGAL COMPRESSOR 6 Claims, 2 Drawing Figs.

521 vs. Cl 415/9 [51] Int. Cl 4 F0lb 25/00 [50] Field of Search 41 5/30,9; ZOO/81.8

[5 6] References Cited UNITED STATES PATENTS 1,326,867 12/1919 Junggren415/9 1,498,096 6/1924 l-lerr.... 415/9 1,832,779 11/1931 Johnson.200/8l.8 2,764,651 9/1956 Lang ZOO/81.8

3,207,473 9/1965 Madden 3,164,368 1/1965 Klein.....

Primary Examiner-Henry F. Raduazo Attorney-Stephen J. Rudy ABSTRACT: Asafety device to protect a rotor impeller in a centrifugal compressorfrom damage that might otherwise occur when the impeller, because ofsome fault, engages an opposed wall ofits chamber. The device includes ahollow tubular body supported in the walls of the compressor. It has onefor the device may be supplied from the compressor system or from anexternal source. In condenser steam turbines, the tubular body of thedevice may be connected with a vacuum element and arranged so that whenthe thin end is abraded away the tubular body will become pressurized bythe process fluid to cause actuation of the pressure switch. I

ROTOR GUARD FOR CENTRIFUGAL COMPRESSOR BACKGROUND OF THE INVENTION Thisinvention is concerned with a safety device for guarding against thedamage that is likely to result in a centrifugal compressor unit as aconsequence of loss of clearance developing between the impeller of itsrotor and an opposed wall of the impeller chamber.

In centrifugal compressor units of the gaseous type having a rotor, theclearance of its impeller relative to the opposed walls of the rotorchamber is normally close. Accordingly, only a very limited loss ofclearance could result in rubbing of the rotating blades of the impelleragainst one of the walls of the chamber with consequent damage.

The objective of the present invention is to provide a compressor unitwith safety guard which extends slightly into its rotor chamber, andwhich is adapted, when a loss of rotor clearance develops sufficientlyfor the impeller of the rotor to contact the guard, to cause operationof a control circuit switch and consequent discontinuance of operatingpower to the rotor.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing wherein theinvention is illustrated:

FIG. 1 is a view in section of a rotor safety guard embodying theinvention installed in a pneumatic centrifugal compressor; only so muchof the compressor being shown as needed for a proper understanding ofthe invention; and

FIG. 2 is a view similar to that of FIG. 1, but showing a modified formof the rotor safety guard.

DESCRIPTION OF A PREFERRED EMBODIMENT Reference is directed to theaccompanying drawing, and now especially to FIG. 1 in which is shown asection of a scroll case of a conventional centrifugal pneumaticcompressor. The case has the usual inlet passage 11 through which air isdrawn by the impeller 12 of a rotor 13, and is compressively dischargedthrough the case. The case defines a narrow space or chamber 14 betweenthe opposed walls 15 and 16 of which the impeller rotates. The impelleris carried at one end of a rotor shaft 17 which is rotatably supportedin conventional manner in a section of the compressor (not shown). Thesupport of the rotor is such that a clearance 18 normally exists betweenthe blade face 19 of the impeller and the opposed wall 15 of theimpeller chamber. Undesirable damage to the rotor and to the scroll caseis likely to occur if, because of some fault, the rotor shouldprogressively take up the clearance 18 and carry the rotating blades ofits impeller into contact with the compressor wall 15.

An advantageous solution to this problem is provided by means of asafety rotor guard 21. The guard is a unit that is separable from thecompressor. It is supported in the compressor in such manner as toproject at its forward end into the im peller chamber 14 opposite to andwith some clearance from the blade face of the impeller. If the rotorshould progressively take up the clearance 18, the impeller willcooperate with the guard 21 to cause actuation of a power controlelectrical switch 22. Actuation of the latter will shut off power to therotor before the impeller can damagingly contact the wall 15.

The rotor guard 21 has a hollow body, generally designated 23, designedto be filled with fluid, such as air, under pressure. It is supportedbetween the wall 15 and an outer wall 24 of the scroll case. The bodyincludes an elongated tube 25. A front end of the tube is sealed bymeans of a cap 26. The cap is formed of readily abradable material, suchas soft metal. Here. it is formed of leaded brass. The cap is fixed, asby welding, upon the end of the tube. The cap has a rear portion 27 ofenlarged diameter which is received in an axial bore 28 of the scrollcase wall 15 and is seated by means ofa shoulder 29 at the bottom of thebore. A terminal portion 31 of the cap having a reduced diameter isfitted in a complementary reduced extension of bore 23 and projectsslightly beyond the wall 15 into the impeller chamber. A narrow passage33 in the terminal portion of the cap is sealed at its outer or forwardend by a thin web or wall 34. The opposite end of passage 33 opens intothe relatively larger interior diameter of the tube 25. The terminalwall 34 of the cap is positioned in the impeller chamber substantiallyparallel relative to the blade face of the impeller. Its arrangement issuch that the thin wall 34 will be ground or abraded away by theimpeller's blades so as to vent the interior of the tube in the event ofan undesirable loss of clearance developing between the rotatingimpeller and the opposed wall 15.

. The tube 25 projects at its opposite end through an opening 35 in theouter wall 24 of the scroll case. A sleeve connector 36 on the tube hasa plug portion 37 threadedly engaged in the opening 35. An O-ring 38seals against leakage of compressor air from the interior 39 of thescroll case around the periphery of the connector. A sleeve nut 41threadedly engaged upon an oppositely projecting portion 42 of theconnector cooperates with a sleeve seal 43 to seal against leakagearound the tube 25 and to frictionally restrain the tube 25 againstendwise displacement from the walls 15 and 24 of the scroll case. Thetightened condition of the sleeve nut compresses the resilient seal 43within the nut into tight frictional engagement with the surface of thetube.

A second sleeve nut 44 and a seal 45 connects the free end of tube 25with piping 46. The latter is connected with the control switch 22 whichis of a conventional pressure type. Here, it is defined by means ofaBourdon Tube 47 connected at one end with the piping 46. The sealedterminal end 48 of the Bourdon Tube carries a switch spring contact 49which it is adapted to close or open in an electrical control circuit51, accordingly, as the terminal end 48 of the Bourdon Tube is caused tobe extended or retracted.

The piping 46 is connected by means of an orifice 52 with a constantsource of pressure fluid 53 whereby the interior of the rotor guard 21is pressurized with fluid and maintained in a constantly pressurizedcondition at a predetermined pressure. In the pressurized condition ofthe rotor guard, the terminal end 48 of the Bourdon Tube is extended sothat the switch contact 49 has a normally closed condition in thecontrol circuit, as appears in FIG. ll.

In summary of the manner in which the rotor guard functions, if, becauseof some fault, the rotor 13 should progressively move toward the wall15, the blades of its rotating impeller will eventually contact andabrade away the thin end wall 34 of the rotor guard to effect venting ofthe interior of the latter. The pressure fluid will in this action dumpthrough the vented passage 33 faster than it wiil enter from the supplysource 53 into the rotor guard through the relatively more restrictedorifice S2. The internal pressure of the rotor guard accordingly relaxescausing the terminal end 48 of the Bourdon Tube to retract the switchcontact 49 to open condition. The control circuit responds to this:action and shuts off operating power to the compressor.

The extent of the projection of the front end of the rotor guard intothe impeller chamber 14 and the thinness of its end wall 34 is such thatthe latter will be ground away and the power to the compressor will becaused to be shut off before the impeller can come into damaging contactwith the compressor wall 15.

The end of the rotor guard projects into the impeller chamber onlyslightly and approximately to the extent of the thinness of the end wall34. Here, the latter has a thickness of about 0.005 of an inch. It isnot necessary that the end wall 34 be fully abraded away. It is onlynecessary that a slight abrading action occur to weaken the end wallsufficiently for the pressurized fluid in the rotor guard to breakthrough.

In FIG. I, it is noted that the cap end 26 of the tube is retained inits seated condition in the wall 15 against endwise displacement bymeans of the compressed condition of the sleeve seal 43 together withthe connector 36. In FIG. 2, a

modified arrangement is provided for maintaining the seated condition ofthe cap end of the tube. In FIG. 2, a relatively shorter tube 25a isprovided. Its rear end is enlarged by means of a collar or piston 54fixed thereon. The collar has a slide fit in a corresponding internalenlargement 55 of the sleeve connector 36a. The rear portion 42a of theconnector is coupled by means of a sleeve nut 41a and a sleeve seal 43ato piping 46a which connects with the pressure control switch. A space56 normally exists between an internal shoulder 57 of the connector andthe opposed end of the collar 54. By means of this arrangement, thepressure fluid in the rotor guard acting against the collar presses andholds the cap end 26a of the tube in its seated condition. An O-ringseals against leakage around the collar 54. An advantage of thisarrangement is that it allows for thermal expansion of the tube 25a thatmight occur as a result of temperature changes developing duringoperation of the compressor. In this respect, the collar end 54 of thetube will move in the space 56 accordingly as the tube is thermallyaffected.

In a multistage centrifugal compressor in which intake fluid is drawnand compressively passed through successive stages, a separate rotorguard unit 21 may be associated with the impeller chamber of each stage;or the chambers of only certain selected stages may be equipped withrotor guards. In such arrangements, the several rotor guards would beconnected in parallel with the piping 46. The latter would be connectedby a single orifice 52 to the common source 53 of pressure fluid andwould be connected to a single control switch 22. it can be seen in suchan arrangement that the control switch would be actuated to shut offpower to the entire compressor should anyone of the rotor guards becaused to be vented by the re lated impeller.

The rotor guard may be pressurized with air or liquid. The source forsuch may be bottled high-pressure fluid; the usual pneumatic orhydraulic control system of the compressor; the compressors lubricationsystem; or the fluid being processed by the compressor. in all cases,the pressure level of the fluid source should be distinctly above thepressures in the impeller chamber at the location of the rotor guard.

in some applications of the rotor guard unit, such as with a condensingsteam turbine, the rotor guard could be connected to the usual condenservacuum instead of to a fluid pressure source. In such an arrangement,when the end of the rotor guard is abraded away, the process fluid willrush into the rotor guard to fill the vacuum. The pressure switch insuch a situation will respond to a sudden pressure rise in the rotorguard instead of to a sudden pressure drop.

The orifice 52, because of its restricted nature, is of furtheradvantage in that it materially limits the quantity of fluid that canescape after the end wall of the cap is vented.

it is understandable that when a rotor guard unit has been acted upon bythe impeller, it may be subsequently readily withdrawn from thecompressor through the opening 35 for replacement after firstdisconnecting the connector 36 and sleeve nut4l.

We claim:

1. in a centrifugal fluid compressor including a rotor carrying animpeller having rotation in a space defined between a pair of opposedwalls of the compressor, one of the walls having a recessed shoulder ina bore opening axially into the space in opposed relation to the bladeface of the impeller, a rotor guard comprising a tubular body having acap fixed over one end and seated upon the recessed shoulder and havinga forward end projecting into the space, a connector supporting anopposite end of the tubular body in further wall of the compressor, afluid pressure switch, piping means connecting the said opposite end ofthe tubular body with the pressure switch, an orifice connecting thetubular body with a constant source of pressure fluid, and a narrowpassage in the cap sealed by means of a thin abradable wall at theforward end of the cap, the passage being relatively larger in diameterthan the orifice, the pressure switch being responsive in a particulardirection to pressurization of theinterior of the tubular body withfluid from the source and being responsive in an opposite direction uponthe thin wall being abraded away to relieve the fluid from the tubularbody through the narrow passage, the impeller being adapted upon losingaxial clearance relative to said one wall to engage and abrade away thethin wall.

2. In a centrifugal fluid compressor as in claim 1, wherein the saidopposite end of the tubular body has a collar disposed with a slide fitpart way into the interior of the connector, the rear end of the collarbeing subject to fluid pressure within the interior of the rotor guardwhereby the cap end of the tubular body is held seated upon the recessedshoulder.

3. In a centrifugal fluid compressor as in claim 2, wherein an O-ringseal is provided about the periphery of the collar having sealingengagement with the surrounding wall of the connector.

4. In a centrifugal fluid compressor as in claim 1, wherein a sleeveseal is fitted upon said opposite end of the tubular body, and a sleevenut threadedly engaging a rear portion of the connector compressivelyengages the sleeve seal into tight en gagement with the tubular body.

5. in a centrifugal fluid compressor as in claim 1, wherein the level ofthe pressure in the rotor guard is greater than the ambient pressure inthe said space of the compressor.

6. A safety guard comprising a hollow tubular body having a reducedpassage at one end and a readily abradable thin wall sealing over theend of the passage, a pressure-responsive switch connected to theopposite end of the tubular body, an orifice the diameter of which isreduced relative to said passage connecting with the interior of thetubular body intermediately of the ends of the latter, the switch beingadapted to respond in a particular direction in response to a relaxedpressure condition developing within the interior of the tubular bodyand to respond in the opposite direction in response to a pressurizedcondition developing within the interior of the tubular body, thetubular body being adapted to be supported in the housing of a rotor ina manner so as to have its abradable wall end project into a rotorchamber in opposed spaced relation to the blade face of the rotorsimpeller, the abradable wall being adapted to be abraded away upon beingengaged by the impeller blades so as to open the interior of the tubularbody through the reduced passage to pressures within the rotor chamber,and the orifice being adapted for selective connection with a suctiondevice or a fluid pressure source.

1. In a centrifugal fluid compressor including a rotor carrying animpeller having rotation in a space defined between a pair of opposedwalls of the compressor, one of the walls having a recessed shoulder ina bore opening axially into the space in opposed relation to the bladeface of the impeller, a rotor guard comprising a tubular body having acap fixed over one end and seated upon the recessed shoulder and havinga forward end projecting into the space, a connector supporting anopposite end of the tubular body in further wall of the compressor, afluid pressure switch, piping means connecting the said opposite end ofthe tubular body with the pressure switch, an orifice connecting thetubular body with a constant source of pressure fluid, and a narrowpassage in the cap sealed by means of a thin abradable wall at theforward end of the cap, the passage being relatively larger in diameterthan the orifice, the pressure switch being responsive in a particulardirection to pressurization of the interior of the tubular body withfluid from the source and being responsive in an opposite direction uponthe thin wall being abraded away to relieve the fluid from the tubularbody through the narrow passage, the impeller being adapted upon losingaxial clearance relative to said one wall to engage and abrade away thethin wall.
 2. In a centrifugal fluid compressor as in claim 1, whereinthe said opposite end of the tubular body has a collar disposed with aslide fit part way into the interior of the connector, the rear end ofthe collar being subject to fluid pressure within the interior of therotor guard whereby the cap end of the tubular body is held seated uponthe recessed shoulder.
 3. In a centrifugal fluid compressor as in claim2, wherein an O-ring seal is provided about the periphery of the collarhaving sealing engagement with the surrounding wall of the connector. 4.In a centrifugal fluid compressor as in claim 1, wherein a sleeve sealis fitted upon said opposite end of the tubular body, and a sleeve nutthreadedly engaging a rear portion of the connector compressivelyengages the sleeve seal into tight engagement with the tubular body. 5.In a centrifugal fluid compressor as in claim 1, wherein the level ofthe pressure in the rotor guard is greater than the ambient pressure inthe said space of the compressor.
 6. A safety guard comprising a hollowtubular body having a reduced passage at one end and a readily abradablethin wall sealing over the end of the passage, a pressure-responsiveswitch connected to the opposite end of the tubular body, an orifice thediameter of which is reduced relative to said passage connecting withthe interior of the tubular body intermediately of the ends of thelatter, the switch being adapted to respond in a particular direction inresponse to a relaxed pressure condition developing within the interiorof the tubular body and to respond in the opposite directioN in responseto a pressurized condition developing within the interior of the tubularbody, the tubular body being adapted to be supported in the housing of arotor in a manner so as to have its abradable wall end project into arotor chamber in opposed spaced relation to the blade face of therotor''s impeller, the abradable wall being adapted to be abraded awayupon being engaged by the impeller blades so as to open the interior ofthe tubular body through the reduced passage to pressures within therotor chamber, and the orifice being adapted for selective connectionwith a suction device or a fluid pressure source.